According to conventional pneumatic yarn splicing method, so-called false twists are imparted to the doubled portion of yarns by a swiring stream of jetted air and in this state, the yarn splicing operation is accomplished. Therefore, S twists are given to one end of the joined portion of yarn and Z twists are given to the other end of the joined portion. Furthermore, twists in a certain direction are given to spun yarn by the spinning operation. Accordingly, on one end of the joined portion, the direction of inherent twists of the yarn is opposite to the direction of twists given by the air nozzle, and in this end portion where twists of opposite compositions are given, fluffs are readily formed and the yarn tenacity is reduced.